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Everybody, John Barnes posted the following amazing article on lugnet.robotics!
In lugnet.robotics, John Barnes writes:
> I received the new 8539 (Manas) in the mail yesterday.
>
> I have not built the models.
>
> But I have taken the receiver unit to pieces and decoded the IR
> messaging scheme ;)
>
> The transmitters transmit short messages of two bytes encoded as
> 8 bit + odd parity. The transmissions use 76kHz modulated IR at
> a baud rate of 4800.
>
> I have a picture of the insides, but I cannot figure out how to upload
> to brickshelf. (Any hints would be appreciated! - I have a username
> but when I login there are no upload buttons or hints.)
>
> Lego have sadly gone back to the cheap battery operated toy type
> motors so there's none of the amazing technic motor efficiency of
> either the technic or micro-scout variety.
>
> It is interesting that there are two power take-offs, one "through axle"
> hole and "end axle" hole at each end of the unit. The two are differently
> geared so you can choose higher speed or higher torque.
The gear ratio between the two types of axle holes is about 5 : 2. (The
"through axle" turns faster.) On a light load (i.e., the big Rahi waves its
arms), the speed is roughly 300/120 RPM.
> The transmitter offers channels 1, 2 or 3 or "All". A little switch must
> set on both the transmitter and the receiver to get correct operation.
>
> Each channel is differentiated by both an address in the message and
> by the rate at which messages are sent. The messages are very short
> in comparison to the time between messages which helps minimize the
> chances of a "collision". The receivers have error checking and simply
> ignore bad messages. Each button press on the transmitter sends a
> continuous stream of messages. When the last button is released, a
> set of three "no buttons pressed" messages are transmitted before the
> transmitter shuts down. If the no buttons pressed message is missed
> by the receiver, it times out after about half a second and turns the
> motors off anyhow.
>
> The messages, which consist of two bytes are best thought of as four
> four bit nibbles.
>
> byte 1 - high nibble : byte 1 - low nibble : byte 2 - high nibble : byte 2
> low nibble
>
> These four nibbles are used as follows;
>
> address : orange : yellow : check
>
> The address nibble can be;
>
> 4 - all
> 5 - Ch. 1
> 6 - Ch. 2
> 7 - Ch. 3
>
> The orange and yellow nibbles reflect the current button state;
>
> 0 - no button pressed
> 7 - forward button
> F - reverse button
>
> The check nibble contains a check digit;
>
> Checkdigit = 0 - (address + yellow + orange)
>
> Thus, for example;
>
> 50 74 is forward yellow button on channel 1
> 6F 0B is reverse orange button on channel 2
> 40 0C no buttons pressed on "All" channel
>
> The message rates are as follows;
>
> Ch. 1 - 19.6 Hz
> Ch. 2 - 14.8 Hz
> Ch. 3 - 11.6 Hz
> "All" - 19.6 Hz
Wow, wow! How did you figure all these out in one day?
> The most interesting part of the whole thing is that the IR receiver looks
> a lot like the
> one in the RCX. Therefor, I decided to test it and was surprised to find it
> responded
> to both 76kHz and 38kHz!
>
> This means that it may be possible to send these two byte messages from the RCX
> to these dual motor units. This would be very very handy.
>
> The secondary reason why I posted this message was to find out if anybody knows
> how to send 4800 baud bytes using nqc. I would like to check if these units
> can be used as auxiliary motors! :)
The firmware does not let you do this, so nqc is out of the questions. Maybe
you can do this in straight C under LegOS. Anybody knows?
> As a matter of note, I have browsed through the parts delivered with the
> "big bits" I've
> already discussed and there are quite a few nice new smooth beams of
> various lengths
> and other little technic parts I haven't seen before. Jim Hughes has some work to do ;)
>
> JB
Cheers,
Hao-yang Wang
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 | | A review of 8539 (Manas)
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| I received the new 8539 (Manas) in the mail yesterday. I have not built the models. But I have taken the receiver unit to pieces and decoded the IR messaging scheme ;) The transmitters transmit short messages of two bytes encoded as 8 bit + odd (...) (25 years ago, 25-Jul-01, to lugnet.robotics)
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